Magnetron and circuit



Sept. 23, 1947.-

c. W. HANSELL 2,427,781

MAGNETRON AND CIRCUIT Filed Feb. 25, 1943 2 Sheets-Sheet 1 Jau/Pcs ,0L/455 (aA/ffm I! Saz/Pre A. C. J7 Henn/v Source IN VEN TOR. (24mm/cs #1,/ Mwvsfu.

BY gwen A TTOR'N E Y Sept. 23, 1,947. c. w. HANSELL MAGNETRON AND C IRCUIT Filed Feb. 25, 1943 2 Sheets-Sheet 2 ATTORNEY Patented Sept. 23, 1947 UNITED STATES PATENT GFFICE MAGNETRON AN D CIRCUIT Clarence W. Hansell, Port Jeerson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application February 25, 1943, Serial No. 477,062

2 generally shown and described in my United States Patent 2,217,745, granted October 15, 194'2. The cathode 3 is, in accordance with the invention, one which is a good secondary emitter but quency magnetron to be used for the production 5 which has low Vemission due `to other causes than of pulses of oscillation, as distinguished from secondary emission. Thus, cathode 43 may be a continuous wave oscillation. cold cathode of cylindrical form, `as described This invention is an alternative arrangement latter in connection with Fig. 3, or be one which for kthe magnetron system disclosed in my cohas associated therewith a thermionic element pending .application Serial No. 470,768, filed Dewhose temperature is relatively low, to reduce cember 3l, 1942, Patent No. 2,409,038, dated Octo thermionic emission, kas described later in rconber 8, 1946. nection with Fig. 2.

Among the objects of the invention are: To In order to understand the operation of the simplify the design yand construction, and remagnetron of Fig. 1 to produce pulses of high duce the weight, bulk and cost of radio systems frequency energy, in accordance with the invenemploying magnetrons for producing pulses of tion and as described in more detail later in high frequency energy; to provide a magnetron reference to the circuit embodiments of Figs. 2, 3 which produces pulses of oscillation in response and 4, there are shown different Aelectron paths to relatively low power control pulses; to prolabeled 4, 5, 5, 7 and 8 Wheh are given OI the vide a novel form of magnetron construction purpose of exposition. which includes a cold cathode capable of pro- If, according to usual practice and theory, the ducing secondary electrons upon bombardment anode to cathode potential is adjusted to be Yless by primary electrons; to produce a magnetron than the cut-off potential, and we assume that which oscillates by virtue of a falling electric eid loss of electrons due to motions parallel to the between the anode and cathode; and to produce axis of the magnetron are prevented due to the a magnetron which oscillates by virtue of a risuse 0I" Suitable eleete and magnete fleld C011- ing magnetic field. iigurations, then ,any electrons leaving the cath- A more detailed description of the invention ode are caused to miss the anode and return to follows in conjunction with drawings, wherein: the Cathode. ApOltOIi Of CheHL-UPOII returning Fig. 1 illustrates in cross-section a magnetron 30 to the cathode, run into negative Space Charges construction with electron paths indicated disu'cient to prevent their re-absorption on the agrammatically for the purpose of explaining cathode. These tend to be more or less Ypermathe principles of the present invention; nently detached from contact with either anode Figs. 2 and 3 schematically illustrate two dif or cathode, and as they increase in number a ferent embodiments of the invention employing rapidly rotating electron space charge will aca falling electric field to produce oscillations; and cumulate in the space between anode and cath- Fig. 4 schematically illustrates a third embodiode. When this space charge becomes dense ment of the invention which employs a rising enough, oscillations `take place. Under the demagnetic eld to produce oscillations, scribed conditions, these oscillations may take Referring to Fig. 1 in more detail, there is 40 place in an uncontrolled manner and may be shown a magnetron construction including :a cyeither' pulsing or continuous, depending upon the lindrica-l cathode 3within an evacuated envelope, magnetron design and the conditions of operawhich envelope comprises a surrounding anode tion.

2 having an even number of anode segments, On the other hand, if the anode-to-cathode and any suitable means such as a permanent potential of the magnetron is somewhat greater magnet or a magnetic field winding l surroundthan the cut-off potential correspo-nding to the ingl the envelope for producing flux lines extendparticular intensity of magnetic eld chosen, then ing parallel to the axis of the cathode. The nearly all electrons which lleave the cathode 3 anode -is composed of an even number of inwill strike the anode (i on the rstoutward trip, wardly protruding anode portions 9, 9 which are 50 following paths qualitatively indicated `by 4 lin substantially or effectively spaced from one an- Fig. 1. Putting it in other words, the direct curother by one-half wavelength at the operating rent potential on the anode is adjusted to be highv frequency of oscillations. This kind of anode, enough to prevent accumulation ofv space charge. which is a preferred type, though not essential For this condition, there is no vaccumulation of inthe practice of the invention, is of the type rotating space charge around the cathode, in-

side the anode, and oscillations cannot take place. Now, if the anode potential is reduced rapidly, as by pulsing, to a value below cut-off (i. e. ,below the value at which all electrons strike the anode on their rst outward trip), then electrons will begin to miss the anode and return to the cathode, following paths qualitatively indicated by in Fig. 1. If the reduction or fall in anode potential is suciently rapid, electrons drawn from the cathode or from the space close to it, while the potential is falling, will circulate out from the cathode and return to the cathode with an excess of energy, striking it and causing the emission of additional electrons due to secondary emission. Each electron returning over path 5 may, for example, cause emission of two secondary electrons which will be drawn out over paths 6, return to the cathode and cause emission of four electrons which traverse path 'I, etc. Thus, while the anode-to-cathode potential is decreasing, there is obtained a rapid growth in total cathode emission due to secondary emission. When, due to the growth of total emission from secondary emission, the total space 4charge has become great enough, high frequency oscillations in the anode structure will start, due to the condition of negative resistance. Once oscillations have reached sufficient amplitude, bombardment of the cathode by incorrectly timed, or out-of-phase electrons can maintain the total cathode emission at a high value without any need for continued rapid reduction of anode potential. Oscillations will then continue indenitely, or until the anode-to-cathode potential drops to a value too low to maintain oscillation. The beginning of oscillation may, in some cases, be made more certain if the downward pulse of anode-to-cathode potential is immediately followed by an upward pulse, or oscillation, so that the whirling electron space charge, after it has grown to great density, is expanded by the rising potential until it reaches out to the anode projections.

Various features of the present invention relate to the input circuit in the form of an energy storage circuit to produce the required high anode potential in excess of the cut-off value; the cathode which is a good secondary emitter but has low emission due to other causes than secondary emission; and to the complete circuit which includes the source of short duration control pulses of low power to pulse the anode potential downwards.

Fig. 2 shows a complete circuit arrangement in accordance with one embodiment of the invention for producing pulses of high frequency oscillation. In Fig. 2, the magnetron construction is substantially the same as that of Fig. 1, except that the cathode, labeled 3 in Fig. 2, is heated by a low frequency heating source (60 cycles or so) over transformer I0 by adjustment of tap II on resistor I2 to a temperature much below the usual operating temperatures of magnetron cathodes and just enough to produce a small priming current of electrons. The anode potential is supplied from a high potential direct current source I3 which is connected between anode and cathode through a charging choke coil I4 and an artificial line I5. A large condenser I6 for by-passing the pulse frequency is connected across the direct current source I3. The artificial line I5, which may have a greater number of sections than has been shown, acts as a storage reservoir input circuit for supplying a potential between anode and cathode which is in excess of cut-off potential. This line storage circuit should have a characteristic impedance which is considerably lower than the input resistance of the magnetron, so that when pulse current through the magnetron starts, the potential does not drop too far but (after a time interval corresponding to the pulse length desired) the potential will change again, due to a wave relected over the line, in a manner to stop oscillation again.

In the condition of anode-to-cathode potential greater than the cut-off potential, all of the electrons emitted by the low heated cathode are drawn to the anode at their rst trip out from the cathode. In order to prevent a large loss due to all the thermionic emission electrons striking the anode, it is proposed to reduce the cathode temperature to such an extent that the thermal emission is very small, less than say one milliampere.

A relatively low power source of control pulses l1, coupled to a transformer I8 in the circuit between the source I3 and the cathode, serves to pulse the anode-to-cathode potential downward; that is, reduce the anode potential at a rapid rate to a value below cut-off potential, in order to start the accumulation of rotating space charge around the cathode and the initiation of oscillations. The downward pulsing of the anode-tocathode potential causes bombardment of the cathode by the priming electrons thermally emitted, which, in turn, produces secondary emission, an increase in total emission and a growth of circulating space charge, as a result of which oscillations will start. Once oscillations start, there is a discharge of the energy stored in the artificial line I5 across the magnetron, as a consequence of which (after a definite time interval determined by the effective length of the line) the anode potential is lowered to a value too low to maintain suicient strength of.oscillations to maintain secondary emission, at which time oscillations stop. The storage circuit (artificial line I5) is then recharged from the direct current source I3 through the relatively large reactance I4, and when the anode potential exceeds out-olf, the foregoing cycle of operations will be repeated.

Preferably, the value of the charging choke coil I4 is made very large, in which case constant current can be made to flow through choke I4 in order to charge the storage circuit I5 and the potential across the magnetron just before a pulse is nearly equal to the potential from source It should be noted at this time that while the storage circuit (artificial line) is being charged and the anode-to-cathode potential is increasing, secondary emission from the cathode is inhibited because electrons emitted due to thermionic emission do not return to the cathode, but when returning stop short of the cathode, as illustrated qualitatively by path 8 of Fig. 1. In order to assure, absolutely, that no sufficient amount of space charge accumulates to allow oscillations to start while the anode potential is increasing, it is preferred that the thermionic emission be reduced by reducing the cathode heating current by an initial adjustment, until oscillations start only due to the control pulses from source I'I. In view of the fact that cathode heating occurs during oscillation, due to cathode bombardment by electrons, the heating current required to start operation may be a certain value, whereas a much lower value (or Zero) heating control pulse. -thenkeptbelow the point at which the cathode ytemperature-rises `high enough to produce substantial thermionic emission. Otherwise, the sysitem of Figs. `2 and 3 are alike and operate in similar manner.

current may -be required after operation vhas started.

yIn-eases -where quick starting of operation is not essential, vthe feature -of -externally heating the cathode-may be omitted, in which case a cold Ycathode canlbe employed, asshown in the embodiment of Fig. 3. The cold cathode 3" of Fig. 3

-canlbe..a solid rod or in the form of a hollow cylinder made of material which has a good secondary emission ratio. In the system of Fig. 3, reliance is had uponthe presence-of va few accidental-electrons at placesvneary the cathode While `the-anode-potential is falling in order to start oscillations.

Such electrons maybe produced by cosmic rays, thermal factors, radio-active materials, light shining on the '.cathode, and

other considerations, to produce the `necessary iewV electrons to cause the rst pulse, afterwhich `thereare residual charges on insulated portions of the cathode surface and-ionization which will maintain emission to start oscillation at every In operation, the input power is The use of a cold cathode (as shown in Fig. 3)

`eliminates theneed of a cathode heating transformer and source of heating energy, andthus decreases lthe complexity, volume, weight and lcost of such a-magnetron system.

An alternative form of magnetron is one in which a relatively small heated auxiliary cathode -is associated with the cold cathode to provide a relatively small but controlled electron emission for initiating growth of secondary emission due lto a falling electric field or a rising magnetic field. Suitable combinations of hot and cold cathodes have beenillustrated in my copending application Serial No. 470,768, led December 31, 1942. In using these previously described compound cathode assemblies for the present invention, means is provided to maintain constantly or momentarily potentials which result in elec- -trons from the hot cathode entering the space .between theanode and cold cathode while the "from 120 cycles per second to 3000 cycles per second. However, for pulse communication systems employing speech, telegraph or facsimile `modulationsl the pulse rate would be above the `highest modulation frequency. Source I'I may be any one'of the known types of pulsers, including a vacuum tube puiser circuit. Such a Vacuum tube pulser circuit would, of course, be employed when thesystem of the invention is used for communication purposes. Byway of example,

the direct current source I3 might supply a potential anywhere in the range from 7500 Volts to 30,000 volts,-depending upon the design of the magnetron. The magnetic eld in the systems of Figs. `1 and 2 is preferably of a constant value and employs a magnetic yoke. `A'coil may be fis `usedto-magnetize the -yoke,"or, if desired, the yoke maybe permanently m-agnetize'd.

V.Fig-4 shows another embodimento'f the invention, wherein there is-employed a constant anodetween anode and cathode Aof the magnetron,

through charging choke I4 and energy storage line I5 similarly to Figs. 2and3,-but the pulsing source l1 and pulse `coupling-transformer I8 of Figs. 2 and 3 is omitted.

The magnetron 'has added to it an internal magnetizing coil'l2l, made lup of two sections, one on each end of the magnetron, of -which only oneis shown in thevcross-sectionof'Fig. 4. An external magnetizing system in the form-of an electromagnet or permanent magnet'is provided as before, to produce an intense magnetic field at right angles to the electric fleldbetween anode and cathode. The externally `applied magnetic field and the anode-to-cathodepotential, are so adjusted that all or nearly all of the electrons emitted from the cathode travel out and strike the anode on the first outward passage.

It now a sufficiently powerful pulse'of current is sent through the internal magnetizing coil, in a direction to increase the magnetic iield between-anode and cathode, the magnetic eld strength will pass up through the out off valve and any electron leaving the'cathode willfbe returned-toit. While in transit from the cathode out toward the anode and back to the cathode, each'electron willbe acted upon by a potential induced by the rising magnetic'eld andvwill return to the cathode with excess velocity and energy. If this energy is made great enough, and the cathode is a good secondary emitter,

Yeach returning electron will vrelease Imore than one secondary electron and there will be a rapid `increase or multiplication intotal electron emission from the cathode while the magnetic field is rising. This'may be made to produce suiicient accumulation of circulating space charge to sta-rt oscillation, afterwhichoscillation will continue and produce itsfown secondary emission, so long as the anode-to-cathode potential is high enough.

For further exposition of the principles of electron acceleration by a rising magnetic field, reference is made to'my copending application Serial No. 474,943,led February 6, `1943,13atent No. 2,412,772, dated December 17, 1946.

To produce the pulses of magnetizing current for initiating oscillation, I have shown in Fig. 4 a commutator type pulser 22 similarto that described in a copending application of Nils E. Lindenblad, Serial No. 479,220, filed March 15, 1943. This pulser 22 'comprises four spaced, equal length, arcuate-shaped metallic segments 25, 2t, 21, 28 placed around a circle. An insulating rotor 29 in the center off the circle moves in the direction of the arrowy and is driven by a motor, not shown. Attached to the insulating rotor at diametrically opposite sides thereof and in xed relation thereto are two metallic brushes 30, 30 each of which isdesignedtobridge the adjacent ends of two adjacentjarcuate segments as thebrush rotates. A condenser"3l is connected between two diametrically positioned arcuate segments 26 and '28. A source 32 of direct current poweris connected to arcuate segment 2l Vand to Yone terminal of magnetizing coil 2l. The other terminal of coil 2l is connected to arcuate segment 25. As the rotor 29 rotates, the condenser 3l charges and discharges in such manner that unidirectional pulses of short duration are passed always in the same direction through the magnetizing coil 2|. Any other means for producing a suitable pulse current might be used. In particular, attention is directed toward arrangements used for magnetic deection of cathode ray beams in television and similar cathode ray beam devices.

What is claimed is:

1. In a magnetron having a magnetic field, an anode, and a cathode characterized by low thermal emission and which emits electrons upon bombardment by primary electrons ata ratio greater than unity, means for establishing large lcathode emission comprising a circuit for establishing a high anode-to-cathode potential of a value suiiiciently high to attract all electrons emanating from the cathode directly to the anode on their first outward passage from the cathode, and means for decreasing this potential momentarily in pulses to a value below that at which all electrons strike the anode on their first passage outward toward the anode, to thereby cause said electrons to return to the cathode and bombard the cathode to'produce secondary electrons, and an output circuit coupled to said anode for abstracting radio frequency energy in pulses repeated at a rate less than the frequency of said radio frequency energy.

2. In a magnetron having a magnetic field, an anode, and a cathode characterized by low thermal emission and which emits electrons upon bombardment by primary electrons at a ratio greater than unity, means for establishing large cathode emission comprising a circuit for producing an anode-to-cathode potential suliiciently high for the anode to absorb all electrons from the cathode on their first passage outward toward the anode, and means for rapidly pulsing this potential momentarily downward to a Value which causes the electrons to take curved paths and bombard the cathode to produce secondary emission from the cathode and an output circuit coupled to said anode for abstracting radio frequency energy in pulses repeated at a rate less than the rfrequency of said radio frequency energy.

3. 1n a magnetron having a magnetic field, an anode, and a cathode characterized by low thermal emission and which emits electrons upon bombardment by primary electrons at a ratio greater tha-n unity, means for establishing large cathode emission comprising a circuit for producing an anode-to-cathode potential suiiciently high for the anode to absorb all electrons from the cathode on their first passage outward toward the anode, and means for rapidly pulsing this potential rst momentarily downward to a potential below that required to absorb all electrons leaving the cathode on their first passage outward, to thereby cause said electrons to take curved paths and bombard the cathode and produce additional electrons by Virtue of secondary emission, and then momentarily upward to expand the whirling electrons to thereby assure the generation of oscillations, and an output circuit coupled to said anode for abstracting radio frequency energy in pulses repeated at a rate less than the frequency of said radio frequency energy.

4. In a magnetron having a secondary emissive cathode with small initial emission and an anode resonant to the operating frequency, means for establishing large cathode emission comprising a circuit for producing an anode-tocathode potential sufficiently high for the anode to absorb all electrons from the cathode on their first passage outward toward the anode, and means for pulsing this potential momentarily downward to a potential below that required to absorb all electrons leaving the cathode on their rst passage outward, to thereby cause said electrons to circulate around said cathode and bornbard it to produce secondary emission, and an output circuit coupled to said anode for deriving pulses of radio frequency energy at a repetition rate less than the frequency of said radio frequency energy.

5. In a magnetron having a non-thermionic secondary emissive cathode and an anode resonant to the operating frequency, means for establishing large cathode emission comprising a circuit for producing an anode-to-cathode potential sufiiciently high for the anode to absorb all electrons from the cathode on their first passage outward toward the anode, and means for pulsing this potential momentarily downward to a potential below that required to absorb all electrons leaving the cathode on their first passage outward, to thereby cause said electrons to circulate around said cathode and bombard it to produce seconda-ry emission, and an output circuit coupled to said anode for deriving pulses of radio frequency energy at a repetition rate less than the frequency of said radio frequency energy.

6. A vacuum tube oscillator of high frquency oscillations having a cathode which emits electrons upon bombardment by primary electrons at a ratio greater than unity and which has low emission qualities due to other causes, an anode structure surrounding said cathode, said cathode extending substantially along the axis of said anode, means for producing a magnetic field having components parallel to said cathode, a source of potential coupled between said anode and cathode for supplying to said anode a potential whose value is so related to said magnetic field and sufficiently large to absorb all electrons on the first passage outward from the vicinity of the cathode, and means for periodically reducing said anode potential below said value necessary to absorb said electrons on their first outward passage, to thereby cause said electrons to circulate around said cathode and bombard it to produce secondary electrons.

'7. A vacuum tube oscillator of high frequency -oscillations having a cathode which emits electrons upon bombardment by primary electrons at a ratio greater than unity and which has low emission qualities due to other causes, an anode structure surrounding said cathode, said cathode extending substantially along the axis of said anode, means for producing a magnetic field having components parallel t0 said cathode, a source of potential coupled between said anode and cathode for supplying to said anode a potential Whose value is so related to said magnetic iield and sufficiently large to absorb' all electrons on the rst passage outward from the vicinity of the cathode, and a pulser circuit operating in the range from 60 cycles per second to 50,000 cycles per second for periodically reducing said anode potential below said value necessary to absorb said electrons on their first outward passage, to thereby cause said electrons to circulate 9 around said cathode and bombard it to produce secondary electrons.

8. A vacuum tube oscillator of high frequency oscillations having a cathode which emits electrons upon bombardment by primary electrons at a ratio greater than unity and which has low emission qualities due to other causes, an anode structure surrounding said cathode, said cathode extending substantially along the axis of said anode, means for producingv a magnetic field whose flux lines extend substantially parallel to said cathode, a source of potential coupled between said anode and cathode for supplying to said anode a potential whose value is s-ufliciently large to absorb all electrons on the rst passage outward Ifrom the vicinity of the cathode, `and an electron discharge device pulser circuit for periodically reducing said anode potential below said value necessary to absorb said electrons on their first outward passage to thereby cause said electrons to take curved paths and bombard said cathode to produce secondary electrons.

9. In a pulse type communication system, a vacuum tube oscillator of high frequency oscillations having a cathode which emits electrons upon bombardment by primary electrons at a ratio greater than unity and which has low emission qualities due to other causes, an anode structure surrounding said cathode, said cathode eX- tending substantially along the axis of said anode, means for producing a magnetic eld having flux lines extending parallel to said cathode, a source of potential coupled between said anode and cathode for supplying to said anode a potential whose value is suiciently large to absorb all electrons on the rst passage outward from the vicinity of the cathode, and an electron discharge device pulser circuit operating at a rate above the highest modulation frequency for periodically reducing said anode potential below said value necessary to absorb said electrons on their first outward passage, to thereby cause said electrons to take curved paths and bombard said cathode to produce secondary electrons 10. A vacuum tube oscillator of high frequency oscillations having a cathode which emits electrons upon bombardment by primary electrons at a ratio greater than unity and which has low emission qualities due to other causes, an anode structure surrounding said cathode, said cathode extending substantially along the axis of said anode, a substantially constant magnetic field having iiux lines extending parallel to said cathode, a source of potential coupled between said anode and cathode for supplying to said anode a potential whose Value isY sufliciently large to absorb all electrons on the rst passage outward from the vicinity of the cathode, and means for periodically reducing said anode potential below said value necessary to absorb said electrons on their rst outward passage, to thereby cause said electrons to circulate around said cathode and bombard it to produce secondary electrons.

11. A vacuum tube oscillator of high frequency oscillations having a cathode which emits electrons upon bombardment by primary electrons at a ratio greater than unity and which has low emission qualities due to other causes, an anode structure surrounding said cathode, said cathode extending substantially along the axis of said anode, a source of potential coupled between said anode and cathode for supplying a voltage to said anode which is positive relative to said cathode, means for supplying a magnetic field having -ux lines extending parallel to said cathode, and

10 means. for pulsing the magneticfield momentarily upward to a value which causes the electrons to curve and return to saidcathodewith sufdi-` cient strength to bombard the cathode and produce secondary electrons.

12. A magnetron having a secondary emissive cathode which emits electrons upon bom-bardment by primary electrons at a. ratio greater than unity and which has small initial emission, means for establishing large cathode emission comprising a circuit for producing an anode-tocathode potential sufficiently high for the anode to absorb all electrons from the cathode on their rst passage outward toward the anode, a circuit for producing asubstantially constant magnetic field, and means for rapidly and repeatedly pulsing this potential momentarily downward. to a value below that required to absorb all electrons on their rst passage outward from the cathode, to thereby cause the electrons to take curved paths and bombard the cathode with suiiicient intensity to produce secondary electrons.

13. In a high frequency magnetron oscillator, means for supplying a substantially constant electric eld between the anode and cathode, said cathode being capable ofA emitting electrons upon bombardment by primary electrons at a ratio greater than unity, means for supplying a magnetic field whose intensity is sufficiently low to permit all electrons in the vicinity of the cathode to lbe absorbed by said anode on the first passage outward, and means for periodically increasing the intensity of said unagneticeld toa value which causes the electrons to curve and return to said cathode with sufficient-intensity to bombard it andl release secondary electrons to thereby permit a growth in number of circulating electrons around said cathode with a consequent initiation of oscillations.

14. In a high frequency magnetron oscillator, means for supplying a substantially constant electric field betweenA the anodev andl cathode, a cathode which emits electrons upon bombardment by primary electrons at a ratio greater than unity and which has low emission qualities due to other causes, means for supplying a magnetic eld whose intensity is sufliciently low to permitall electrons in' thevicinity of the cathode to be absorbed by said anode onV the first passage outward, and Vmeans for periodically increasing the intensity of said magnetic field to a value which causes the electrons to curve and return to said cathode with sufficient intensity to bombard it and release secondary electrons to thereby permit the growth of circulating electrons around said cathode with a consequent initiation of oscillations.

15. The method of operating an electron discharge device oscillator having a secondary emissive cathode which emits electrons upon boimbardment by primary electrons at a ratio greater than unity and which has low emission qualities due to other causes, an anode and a substantially constant magnetic iield parallel to said cathode, which includes impressing on said `anode a potential in excess of oscillation cut-olf Value, and periodically reducing said potential rapidly to a value below the cut-off Value to cause the electrons to take curved paths and bombard the cathode with sumcient strength to release secondary electrons therefrom, and deriving radio frequency energy from said oscillator in pulses at a repetition rate less than the frequency of said radio frequency energy.

16. The method of operating an electron dis- 11 charge device oscillator having a secondary emissive cathode which emits electrons upon bombardment by primary electrons at a ratio greater than unity and which has low emission qualities due to other causes, an anode and a substantially constant magnetic eld parallel to said cathode, which includes impressing on said anode a potential in excess of oscillation cut-01T value, and periodically reducing said potential rapidly to a value below the cut-off value and at an audio frequency rate to cause electrons to curve and strike the cathode with sufficient strength to release secondary electrons therefrom, and deriving radio frequency energy from said oscillator in pulses at a repetition rate less than the frequency of said radio frequency energy.

17. The method of operating an electron discharge device oscillator having a secondary emissive cathode, said cathode being capable of emitting electrons upon bombardment by primary electrons at a ratio greater than unity, an anode and a magnetic field parallel to said cathode, which includes impressing a substantially constant anode-to-cathode potential on said oscillator, and periodically raising the intensity of said magnetic iield to a value in excess of that needed to prevent all electrons in the vicinity of said cathode from striking said anode on their first passage outward, to thereby curve the paths of said electrons to produce bombardment of said cathode and emission of secondary electrons from said cathode.

18. A vacuum tube magnetron oscillator of high frequency oscillations having a cathode which emits electrons upon bombardment by primary electrons at a. ratio greater than unity and which has low emission qualities due to other causes, an anode structure surrounding said cathode, said cathode extending substantially along the axis of said anode, means for producing a magnetic eld having ux lines extending substantially parallel to said cathode, a source of potential including a storage circuit coupled between said anode and cathode for supplying to said anode a potential Whose value is su'iciently large to absorb all electrons on the rst passage outward from the vicinity of the cathode, and means for periodically reducing said anode potential below said value necessary to absorb said electrons on their rst outward passage to thereby cause said electrons to take curved paths and bombard said cathode to produce secondary electrons.

19. A vacuum tube magnetron oscillator of high frequency oscillations having a cathode which emits electrons upon bombardment by primary electrons at a ratio greater than unity and which has low emission qualities due to other causes, an anode structure surrounding said cathode, said cathode extending substantially along the axis of said anode, means for producing a magnetic field having ux lines extending substantially parallel to said cathode, a source of potential including a line storage circuit coupled between said anode and cathode for supplying to said anode a potential whose value is sufoiently large to absorb all electrons on the first passage outward from the vicinity of the cathode, said storage circuit having a characteristic impedance which is considerably lower than the input resistance of said magnetron, and means for periodically reducing said anode potential below said value necessary to absorb said electrons on their first outward passage to thereby cause said electrons to take curved paths and bombard said cathode to produce secondary electrons.

20. A magnetron oscillator of high frequency oscillations having a cathode which emits electrons upon bombardment by primary electrons at a ratio greater than unity and which has low emission qualities due to other causes, an anode structure surrounding said cathode, said cathode extending substantially along the axis of said anode, means for producing a magnetic field having flux lines extending parallel to said cathode, means for producing an electric field between said anode and cathode, said fields being so adjusted that electrons are absorbed by said anode on their rst passage outward from said cathode, and means for periodically changing the value of one of said elds rapidly in such direction as to curve said electrons and cause them to return to and bombard said cathode to release secondary electrons, said last means including a line storage circuit coupled between said anode and cathode and a pulser.

CLARENCE W. HANSELL.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,037,799 Koch Apr. 21, 1936` 2,037,977 Hansell Apr. 21, 1936 2,103,362 Hansell Dec. 28, 1937 2,121,360 Malter June 2l, 1938 2,211,091 Braden Aug. 13, 1940 2,211,404 Braden Aug. 13, 1940 2,230,108 Gerhard Mar. 28, 1941 

